This paper concerns non-isothermal flow in a thermoset resin-injection pultrusion process. Supported by temperature measurements from an industrial pultrusion line and a material characterisation study (curing kinetics, chemorheology, and permeability), the material flow was analysed for the manufacture of a thick glass-fibre profile saturated with a pultrusion-specific polyurethane resin. A central finding is that the heating configuration, together with the strongly convective flow near inlets resulted in phase transitions that were both concave and convex-shaped. This is different from existing literature that commonly describes curing being initiated from die-walls, resulting in the concave phase-transitions.

Process-induced stress and deformation are critical factors when ensuring product quality and structural integrity of composite profiles manufactured using thermoset pultrusion processes. In this paper, we present a new steady-state 3D-Eulerian numerical framework that enables 9–35 times faster computations compared to the current state-of-the-art quasi-static 3D-methods. In addition, we show how process-induced effects from the profile-advancing pulling force and an initial compressive stress state can be modelled. We demonstrate in theoretical parameter studies that the pulling force advances die-detachment and reduces die-swelling, while the initial compressive stress state has the opposite but a more pronounced effect.

The exothermic reaction and overheating during radical polymerization of an Elium® resin and glass fiber reinforced Elium® composites are critically evaluated in this work. The polymerization kinetics of the Elium® resin is obtained by performing differential scanning calorimetry (DSC) scans. The measured data is fit to a temperature and degree of polymerization (DoP) dependent kinetics model. A coupled thermo-chemical process model is developed to predict the temperature evolution and DoP. First, the model is validated with the water bath experiments in which the pure Elium® resin is polymerized at different temperatures (30, 50 and 70 °C). The validated process model is then applied to a vacuum infusion process of glass reinforced Elium® composite laminates with different thicknesses (3.8, 7.5 and 11.3 mm) at room temperature. The produced laminates have the void content lower than 1%. The peak temperature is found to be approximately in the range of 155-160 °C during the water bath experiments. On the other hand, the peak exothermic temperature is approximately 49 °C and 70 °C for 3.8 mm and 11.3 mm thick laminate, respectively. The developed polymerization kinetics model is found to be effective as the predicted temperature evolutions match well with the measured temperatures for different laminates. The effect of laminate thickness and processing teperature on the peak temperature is studied by the developed numerical model. The thermo-chemical process model developed in this work is therefore capable of predicting the polymerization overheating for Elium® composites and can enable the optimization of the manufacturing process to control the thermal and DoP histories.

The resin injection pultrusion is an automated composite manufacturing method in which the resin is injected in a chamber. The flow and the thermo chemical mechanical (TCM) models have been studied for the pultrusion process to improve the reliability of the final products. Flow models are needed to understand and describe the fiber impregnation, filling time and presence of dry spots or voids. Also pressure field in the injection chamber can be estimated with flow models. TCM models are needed to predict residual stress distributions and to optimize the process conditions. A non-uniform fiber distribution strongly affects the results of both types of models. In this study, different strategies are carried out to implement non-uniform fiber distributions into the models. The cross-sectional image and fiber distribution of a 19×19 mm glass fiber reinforced polyester unidirectional pultruded composite is used. Non-uniform fiber distribution is observed and implemented into the flow model by means of permeability variations. The results of this study are compared with uniform fiber distribution results. In the TCM model, the non-uniform fiber volume content is implemented within different sized patches. The results show that the non-uniform fiber fraction should be taken into account for the process models of composites in order to capture the local process induced stresses and probability of dry spots or voids due to poor fiber impregnation.

Process induced stresses inherently exist in fiber reinforced polymer composites particularly in thick parts due to the presence of non-uniform cure, shrinkage and thermal expansion/contraction during manufacturing. In order to increase the reliability and the performance of the composite materials, process models are developed to predict the residual stress formation. The accuracy of the process models is dependent on the geometrical (micro to macro), material and process parameters as well as the numerical implementation. Therefore, in order to have reliable process modelling framework, there is a need for validation and if necessary calibration of the developed models. This study focuses on measurement of the transverse residual stresses in a relatively thick pultruded profile (20×20 mm) made of glass/polyester. Process-induced residual stresses in the middle of the profile are examined with different techniques which have never been applied for transverse residual stresses in thick unidirectional composites. Hole drilling method with strain gage and digital image correlation are employed. Strain values measured from measurements are used in a finite element model (FEM) to simulate the hole drilling process and predict the residual stress level. The measured released strain is found to be approximately 180 μm/m from the strain gage. The tensile residual stress at the core of the profile is estimated approximately as 7-10 MPa. Proposed methods and measured values in this study will enable validation and calibration of the process models based on the residual stresses.